Innate defense against HIV (65%) Infection of cellular targets by HIV is aided and abetted by the proficiency of HIV in eliminating or neutralizing host cell-derived defensive molecules. Among these innate protective molecules, a family of intracellular apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like (APOBEC) cytidine deaminases is constitutively expressed, but inactivated by HIV viral infectivity factor (Vif). Type I Interferon, a cytokine with a plethora of functions in innate and adaptive immunity and a potent inhibitor of HIV in vitro and in vivo, exerts its anti-viral activity, at least in part by inducing APOBEC3 family members. The ability of IFN to augment cytidine deaminases offered the possibility that the balance between virus and target cell might be altered in favor of the host. Untreated HIV-infected volunteers without viral hepatitis received weekly pegylated IFNalpha2a for 12 weeks (NIAID collaboration). Based on these clinical studies, peg-IFN has significant anti-HIV activity in HIV-mono-infected patients and this anti-HIV effect correlated with 2,5 oligoadenylate synthetase (OAS) protein and IFN inducible genes (IFIG). We examined the mechanisms of reduced viral burden by evaluating specific IFIG and their contribution to inhibition of HIV, including APOBEC, BST/tetherin, and TRIM22. Although IFN therapy reduces viral burden in HIV infected individuals, this cytokine can also cause immune dysfunction and toxicities, limiting its use. Through detailed mapping of IFN receptor binding sites, we collaboratively generated IFN hybrids and mutants(NIAID)and determined that structural changes in helix C that influence receptor interactions alter its ability to limit retroviral replication. Our data show a differential ability of IFN constructs to block HIV replication, and the directional magnitude of HIV inhibition correlated with levels of APOBEC3 gene expression. As a marker of toxicity, we demonstrated that certain mutants induced reduced expression of indoleamine 2,3-dioxygenase (IDO) compared to parental IFN. Subsequent to binding with distinct affinities to the common type I IFN receptor complex (IFNAR), the mutants trigger discreet or shared intracellular signaling pathways (Jak/Stat/PI3K/NFkB) leading to antiviral regulation that may be dissociated from underlying toxic effects. By exploring structure and function of IFN relative to its ability to induce APOBEC and other anti-viral molecules, it may become possible to design novel IFN-related molecules, which preserve its beneficial roles in anti-viral and anti-tumor activity while reducing toxicities that arise in the clinical administration of this potent immunomodulator. Regulation of Innate Factors by Mycobacterium avium Perpetuates Survival in Macrophages(35%) Mycobacterium avium complex (MAC) is an environmental microorganism that causes opportunistic infections (OI) in immunocompromised hosts, but rarely causes illness in healthy individuals. Absence of a properly functioning acquired immune response in HIV+ individuals allows M. avium progression and persistence within macrophages. Also, immune reconstitution inflammatory syndrome (IRIS) with a transient focal manifestation of M. avium complex (MAC) of variable duration after the initiation of antiretroviral therapy has been increasingly reported in HIV-1 infected individuals. Importantly, the use of TNF blockers for the treatment of autoimmune diseases has also led to an increased risk of infection/reactivation with various mycobacteria species. Macrophages are essential in controlling M. avium infection, but can become heavily infected in a situation of reduced CD4+ IFN-producing T cells as occurs in AIDS patients. While considered a consequence of deficiencies in IFN, it is still unclear how M. avium averts innate immunity. Infiltration and retention of macrophages in infected lymph nodes (LN) reflect active recruitment. In vitro infection of macrophages with M. avium induces the transcription of IL-17, consistent with the presence of elevated IL-17 in co-infected LN despite the reduced number of T cells. Although not normally associated with macrophages, increased IL-21 gene expression by infected macrophages can perpetuate IFN unresponsiveness by sustaining suppressors of cytokine signaling (SOCS) expression. These data suggest that induction of IL-17 and IL-21 by M. avium in its macrophage hosts may, in part, enable the requisite critical mass of macrophages to harbor and propagate mycobacterial infections.